The present invention relates to a coordinate measuring machine and a method for reliably monitoring a parameter, in particular a moment of inertia, or a mass, required for determining a kinetic energy of an object that can be measured by means of a sensor of a coordinate measuring machine, the object being moved between various positions, wherein the object preferably is briefly at rest in each of the positions.
Coordinate measuring machines are generally known. Coordinate measuring machines are used for measuring workpieces of greatly varying dimensions, and consequently of greatly varying masses, or mass moments of inertia. DE 101 24 493 A1 describes an exemplary coordinate measuring machine with a measuring head, which is movable in relation to a workpiece within a defined measurement volume. The measuring head is used for measuring measuring points defined on a workpiece. For this purpose, the workpiece is brought into a corresponding measuring position in relation to the measuring head. The measuring head often has a probe sensor, in particular in the form of a stylus with a spherical free end, with which the desired measuring points on the workpiece are physically contacted. Therefore, such a measuring head is often referred to as a probe head. Alternatively, there are measuring heads that can be used for contactlessly measuring defined measuring points on a workpiece, in particular with optical sensors.
A control and evaluation unit determines from the position of the measuring head within the measurement volume, and possibly from the position of the probe sensor in relation to the measuring head when probing the workpiece, spatial coordinates that represent the probed measuring point. If the spatial coordinates are determined at a plurality of measuring points, geometrical properties of the workpiece can be measured, such as the diameter of a bore or the spatial distance between two geometric elements of the workpiece. In addition, with a plurality of spatial coordinates it is possible to determine measurement curves that represent the spatial shape of individual geometric elements, or even the spatial shape of the entire workpiece. Often, geometrical dimensions such as the diameter of a bore or the distance between two geometric elements are determined for the first time on the basis of the measurement curves. This determination is equivalent to a scanning operation. Upon “scanning” measured values are adopted during a movement. The probe sensor is in this case in contact with the workpiece, which is thus probed.
Often, turntables are also used, with the workpieces mounted on a moved spindle rather than positioned on the fixed measuring table. During a rotation of the workpiece (and of the corresponding workpiece holder) a specific rotational energy of the rotated object is obtained in dependence on a speed of movement and a moment of inertia.
For safety reasons, such as personal protection, this energy must not exceed certain limit values. Machine guidelines prescribe, for example, an upper limit of 4 J, which must not be exceeded. Otherwise, in the event of a collision, there could be a serious risk of injury to an operator. There is a collision in case, for example, the workpiece and/or the workpiece holder touches or catches a limb of the operator during movement.
This causes the following problem. Since a mass, or a moment of inertia, of a workpiece to be measured is usually not known in advance, the worst, but intrinsically safe case, must be assumed. This means that a maximum speed at which the workpiece and/or the workpiece holder may be moved is fixed on the basis of the greatest possible movable mass, or based on a corresponding moment of inertia. This results in that lighter workpieces are moved unnecessarily slowly. Since many end users mostly measure lighter workpieces, a measuring capacity of the coordinate measuring machine is decreased considerably.
Providing light barriers around the measurement volume or using pressure mats can be seen as a known safety feature. If one of the light barriers is interrupted, present speed of movement is reduced to a safe level. Such solutions are expensive, since, depending on the type of coordinate measuring machine, barriers have to be provided on up to five sides of the machine. Furthermore, the working area of the coordinate measuring machine is increased unnecessarily, since the light barriers have to be installed at a predetermined distance from the workpiece in order that the workpiece can be slowed down before the operator reaches the workpiece after breaking through the light barriers. Furthermore, when using light barriers there is still a certain residual risk, since the operator can possibly also be “trapped” intentionally by the light barriers if, for example, the coordinate measuring machine is operated by two operators. Furthermore, safety devices such as light barriers or pressure mats are troublesome, because the coordinate measuring machine is continually changing its speed, which can have adverse effects on scanning operations.
It is also known to determine the mass automatically by means of pressurized air bearings, as disclosed, for example, in the document DE 100 06 876 C1.
Often, operating instructions of the coordinate measuring machines also contain tables or formulae that can be used for an initial approximate determination of the speed on the basis of a workpiece mass. With this safety concept, there is the problem of a foreseeable misuse or mistake since the moment of inertia is often unknown.
Therefore, it is an object of the present invention to provide a coordinate measuring machine method for reliably monitoring a parameter that represents a measure of the kinetic energy of the moved object.